(1) Field of the Invention
The present invention relates to an image reading apparatus for reading an image on a document using a so-called sheet-through type reading, a method for reading an image, and a storage medium.
(2) Description of the Related Art
In view of convenience for users, in recent years, for image reading apparatuses provided in image forming apparatuses such as copiers, the movable optical system has been adopted, in which an image on a document is read while an optical system is moving below the document placed on a platen glass, and in addition to the movable optical system, the sheet-through type has been increasingly available in the market. In the sheet-through type, an optical system stays below a platen glass, and an image on a document is read while being led by an automatic document feeder (ADF) through a reading location on the upper face of the platen glass.
For example, Japanese Patent Application Publication No. H08-123157 has disclosed a sheet-through type image reading apparatuses, in which a document is transported while floating above the platen glass in order to prevent image streaks caused by foreign substances, such as paper particles from the document, remaining on the platen glass.
However, when a document floats above the platen glass, the floating amount from the platen glass varies depending on the paper type such as thin paper having a high permeability and firm thick paper. Thus, when the floating amount varies, density unevenness and the like slightly occur. Accordingly, it is difficult to uniformly read documents.